The present invention relates to an improved ink jet printing apparatus including an ink ejection means for ejecting ink through a nozzle into an ink jet which is broken into ink drops, a charge electrode for charging the ink drops in response to printing signals, deflection electrodes for deflecting the charged ink drops, and a recording medium conveying means for conveying a recording medium upon which said charged ink drops impinge.
In such an apparatus, the print position is determined in accordance with the charging amount on the ink drop. Supposing that the recording medium to be printed is partially charged, the positions printed by the ink drops fall into disorder depending upon the charged condition on the recording medium, so that the printed image of high quality may not be attained.
In the prior art, a method of uniformly charging the surface of the recording medium or neutralizing the charge on the recording medium has been proposed in order to eliminate the afore-mentioned defect. However, in the case that a recording paper is used as the recording medium for printing image, the states of charging differ from each other in accordance with humidity so that a constant and stable image may not always be reproduced. And, even in the case of neutralizing the charge on the surface of the recording paper by uniformly discharging said charge by means of a corona charger, the quality of the recording paper is not always uniform, so that an inequality in charging partially appears and in consequence the print position may not be precisely fixed. The position may vary with the quality of the recording paper which is not always constant. Therefore, the initially expected object could not be sufficiently accomplished.
Furthermore, the respective diameters of printed dots become different depending upon the flying velocity of the ink drops at the moment of their collision against the recording paper and a distortion of the printed image occasionally appears as the recording paper is frictionally charged. This happens when the recording paper is not tightly attached to the recording paper conveying means, and especially when the leading edge of the recording paper separates from the recording paper conveying means.